The short answer
Enough — but matched to everything else. Plants need light to grow, but light only works in balance with nutrients and CO2. Easy low-tech plants thrive on modest light for 6–8 hours a day; demanding plants and carpets need strong light plus CO2 and dosing. More light on its own doesn’t grow better plants — past a point it just grows algae.
Match light to your plants
There are really two settings:
- Low light / low-tech: easy plants — Java fern, Anubias, crypts, mosses — do beautifully under a modest LED and no CO2. Keep it gentle and they stay green and algae-free.
- High light / high-tech: carpets like dwarf baby tears, red stems and dense scapes need strong light — but only alongside CO2 and full dosing, or the tank tips straight into algae.
See our best planted-tank lights and the lighting hub.
More light isn’t the answer
The most common mistake is reaching for a brighter light when plants struggle. Light is the accelerator, not the fuel. If nutrients or CO2 are the limiting factor, extra light just hands the surplus to algae. When plants stall, check feeding and CO2 before turning up the light — often that’s the real fix.
Get the balance right
Think of light, nutrients and CO2 as a three-legged stool — the weakest leg sets the pace. For low-tech tanks, keep all three modest and matched. For high-tech tanks, raise all three together. See why plants aren’t growing and algae on plants for how the balance plays out.